The United States, the Middle East and world oil markets are bracing for Iran’s response after President Donald Trump launched punishing strikes on Iranian nuclear energy sites overnight, plunging the region into an unprecedented new phase of a decades-old conflict.

The U.S. struck Iranian nuclear facilities, including the key Fordo site, with 14 GBU 57s, 30,000-pound "bunker buster bombs,” according to the U.S. military. It was the first time the United States has directly bombed the Islamic Republic.

The next 48 hours are of particular concern, according to two defense officials and a senior White House official. It’s unclear whether any retaliation would target overseas or domestic locations, or both, the officials said.

U.S. bases and assets have been at their highest state of alert for months, but after Israel began warring with Iran on June 13, the officials, who spoke earlier in the week, said concerns were heightened even more about the potential for attacks on U.S. assets from Iran or its proxies in the region.

Iranian Foreign Minister Abbas Aragchi, meanwhile, warned of “everlasting consequences.”

Iran has already shown its capacity to inflict damage on its enemies.

Since Israel's initial attack on Iran's nuclear facilities, Iranian missiles have pierced the country’s vaunted missile-defense system, the Iron Dome, reduced apartment blocks to rubble, and killed at least 24 people. After the U.S. attacks, the nation launched a missile barrage into Israel Sunday morning, causing damage and injuries in Tel Aviv.

“Iran will try to redouble its efforts against Israel in order to show its determination to inflict damage on its arch enemy," Fawaz Gerges, a professor of international relations at the London School of Economics, said. "We are likely to witness major escalation between Iran and Israel in the next few days.”

However, Gerges added, Iran will try and avoid “being dragged into an all-out war with the United States.”

Iran's Revolutionary Guards argue that the sheer number and spread of U.S. bases in the region, where it has some 40,000 forces, are not a strength, but a “point of vulnerability.”

The U.S. has bases in Iraq, Kuwait, Qatar, Bahrain, and the United Arab Emirates, among other countries. Last week it moved some aircraft and ships that may be vulnerable to a potential attack, and has limited access to its al-Udeid Air Base in Qatar.

It’s unclear whether Iran could retaliate with missile attacks on U.S. or allied forces in the Gulf. Israel has managed to intercept many of the ballistic missiles and drones that Iran has fired over the past week.

And it's also uncertain whether any retaliation will come directly from Tehran or one of its proxies in the region.

Israeli security forces at the site of an Iranian strike that hit Ramat Aviv in Tel Aviv on Sunday. (Jack Guez / AFP via Getty Images)

Iran has long relied on asymmetric tactics against stronger foes, including terrorist attacks. In 1983, the U.S. accused Iran of orchestrating the bombings of a Marine barracks and embassy in Beirut through its Lebanese proxy, Hezbollah, killing hundreds.

Iran has also threatened to block Strait of Hormuz between Iran and Oman, which is a critical international shipping choke point: a fifth of global oil passing through its narrow waters. Blocking it could send oil markets into chaos — but would also hurt Iran’s own struggling economy and alienate neutral powers.

Constraints

Iran’s capacity to strike is narrower than it once was.

Dr. H.A. Hellyer, a senior associate at the London-based Royal United Services Institute, told NBC news that Iran still has the power to attack, “but only because Israelis haven’t taken out all of their missile launchers.”

Iran still has around 40% of its launchers, Hellyer said, "so the threat hasn't been removed in that regard, but they've been degraded quite a lot."

On Sunday, Defense Secretary Pete Hegseth said that while the U.S. did not want war, it will “act swiftly and decisively when our people, our partners or our interests are threatened.”

While Hegseth also said that Iran's nuclear ambitions had been “obliterated,” it will be difficult for the Pentagon to verify that claim without having U.S. forces on the ground. In hours since the strikes, Iran’s state media has downplayed the damage on nuclear facilities at Fordo, Natanz and Isfahan.

With fewer reliable partners in the Middle East and little regional appetite for a wider war, experts warn that Tehran faces a narrower set of options, and a sharper set of risks, as it weighs how to respond.

“They’re really stuck,” said Hellyer. “If they fight back by striking American targets, then the U.S. is very likely to respond with a much more aggressive and continual campaign that could cause even more damage, not only to the regime, but to the country at large.”

“But if Iran doesn’t respond, the cohesion of its regime," a ruling class weighed down by corruption, public discontent, and growing disillusionment with its promises of resistance, "could really be challenged," he added.

Iran's proxy network has also been battered by years of attrition with Israel and the U.S.

Its most important ally, Hezbollah in Lebanon, has been devastated by a series of Israeli attacks and assassinations, and had indicated it would not join the fight against Israel.

The Houthis, Hezbollah, and Iraqi Shiite militias are unlikely to have much impact on the struggle between Israel and the U.S., and Iran. In the Palestinian enclave of Gaza, Hamas — which Iran armed and trained — has been badly weakened and its leaders have been killed.

Iran may also lack staunch support from its neighbors. Some Gulf nations, including Bahrain, Qatar, and the United Arab Emirates stopped short of condemning the U.S. attacks on Iran, calling instead for de-escalation

“The rest of the region is very opposed to this war and doesn’t want it and didn’t want it, but they’re also not able to affect the outcome,” noted Hellyer.

As a result, an increasingly isolated Iran has “no friends to speak of,” he said.